This invention relates to adhesive blends comprising a hydrophilic pressure sensitive adhesive and a hydrophobic pressure sensitive adhesive, more particularly to dry- and wet-surface adhesion, which may be present in different layers in a multilayer structure.
Pressure-sensitive adhesive (PSA) tapes have been used for more than half a century for a variety of marking, holding, protecting, sealing and masking purposes. Pressure-sensitive adhesive tapes comprise a backing or substrate, and a pressure-sensitive adhesive. Pressure-sensitive adhesives require no activation other than finger pressure, exert a strong holding force and should be removable from a smooth surface without leaving a residue.
Adhering to skin presents challenges to adhesive manufacturers due to the inherent variability of the properties of skin. Adhesion to skin is dependent upon many factors. These factors include but are not limited to the environment in which the recipient is located. For instance, adhesion to skin will vary on the same person depending upon the humidity. If the same person were tested for skin adhesion using a given adhesive in different climates, different adhesion results would be obtained depending upon if the person were located in an arid versus in a humid environment.
Furthermore, skin varies from individual to individual. One person may have extremely dry skin whereas another person may have oily skin. As well as varying from individual to individual, skin properties may vary on a given individual depending upon the location on the body. For instance, skin located on a hand may be considerably drier than skin located on a back or face. Therefore, it is very difficult to manufacture a skin adhesive that is suitable for environmental and individual variabilities.
Adhesive composition and performance are also dependent upon the intended use of the adhesive. Use of PSAs for masking tape, or pavement markings will differ from uses for medical applications. While all applications require some wet-stick capabilities, there will be different requirements for the applications. For example, some uses require a gentle adhesive, such as adherence to a sensitive area whereas other uses require a more aggressive adhesive, such as when it is necessary that the adhesive remain adhered for an extended period of time or if the adhesive is adhered to an area which is very mobile.
Medical adhesives are generally used in wound dressings, surgical drapes, bandages and tapes. These items are generally constructed of a backing coated with an adhesive. The performance of the adhesive is in part dependent upon the occlusivity of the backing. Backings are generally categorized by their porosity into either nonocclusive or occlusive backings. When occlusive backings are used to prepare bandages or the like for medical applications the resulting bandage typically does not adhere well to skin over extended time periods. This probably occurs because the bandage cannot release water vapor that causes retention of moisture and in turn causes the adhesive to lift from the skin.
Conformability and cohesiveness are inversely related properties and are considered when preparing or selecting adhesives for end-uses, particularly for medical articles and medical applications. It is desirable for a medical adhesive to conform to the terrain of the skin to which it is adhered. This enhances comfort to the wearer and also ensures a higher initial adhesion to the skin because the adhesive is able to flow into the skin""s topography. However, if an adhesive is too conformable it may lack the necessary cohesiveness necessary to remove the article with the adhesive intact. If an adhesive lacks cohesive strength the adhesive on a bandage may split upon an attempt to remove the article leaving some adhesive residue adhered to the skin and some adhesive removed along with the bandage backing. This is unacceptable to most medical professionals and patients.
Pressure-sensitive adhesives require a delicate balance of viscous and elastic properties that result in a four-fold balance of adhesion, cohesion, stretchiness and elasticity. Pressure-sensitive adhesives generally comprise a polymer that is either inherently tacky or can be tackified with the addition of tackifying resins. They can be coated in solvent or as water-based emulsions to reduce the material viscosity to a level that is easily applied to a substrate of choice.
Generally, when additives are used to enhance properties of pressure-sensitive adhesives they are required to be miscible with the pressure-sensitive adhesive or to have some common blocks or groups to permit homogeneous blends to form at the molecular level. Pressure-sensitive adhesives have been modified to extend their applicability into new areas. Tackified thermoplastic elastomers have been dissolved in acrylic monomers and subsequently cured. Tackified thermoplastic elastomers have also been added to polymerized acrylic pressure-sensitive adhesives in solvent where each component contains a common segment to permit compatibility. Natural rubber has been added to polymerized acrylic pressure-sensitive adhesives in solvent and subsequently thermally cured. The general purpose is to combine the high shear properties of elastomers with the high tack performance of acrylics to achieve adhesion to both polar and nonpolar surfaces. Further improvements and better balance of properties continue to be sought.
Pressure sensitive adhesives that adhere to wet or moist surfaces, so-called hydrophilic or xe2x80x9cwet-stickxe2x80x9d adhesives, are useful in many industrial, commercial and consumer applications. In pharmaceutical and other medical fields, such hydrophilic adhesives are typically used for adhering articles such as tapes, bandages, dressings, and drapes to moist skin surfaces such as wounds or areas of the body prone to moistness. Hydrophilic adhesives also find use in outdoor or exterior applications, such as on roadway materials, traffic control signage, and marine or automotive coatings and surfaces. Labels for food containers and other products that are exposed to moisture due to condensation or subjected to water or ice immersion also must be coated with hydrophilic adhesives.
(Meth)acrylate pressure sensitive adhesives are attractive materials for many tape and label applications because of their hydrophilic character. Copolymerization of (meth)acrylate monomers with hydrophilic acidic comonomers can increase hydrophilic characteristics and can enhance the cohesive strength of the PSA. However, this increased cohesive strength generally diminishes the tack of the hydrophilic acidic comonomer-containing (meth)acrylate copolymer.
At higher acidic comonomer levels, (meth)acrylate copolymers can dramatically lose their tack and become highly hydrophilic. When exposed to water, the moisture helps to transform these highly acidic, low tack compositions into tacky materials that are suitable as wet-stick adhesives used in many medical applications. When the water is allowed to evaporate, these adhesives lose their pressure-sensitive tack. Such compositions can also be useful as water-soluble or water dispersible adhesives. Water-dispersible or soluble (meth)acrylate copolymers can be formulated as repulpable adhesives used to splice dry paper rolls and designed to lose adhesive integrity and fully degrade when undergoing paper recycling operations.
When using high levels of acidic comonomers, it is difficult to effectively copolymerize these materials without a solvent, an aqueous reaction medium, or additives that promote interpolymerization of these monomers. Attempts to copolymerize these monomers in the absence of compatibilizing reaction media often results in heterogeneous materials dominated by glassy regions formed by the polymerization of the acidic comonomers and softer domains comprising the polymerized (meth)acrylate monomers. Thus, (meth)acrylate copolymers having high levels of acidic comonomers have traditionally been made using either solvent or water-based polymerization methods.
Briefly, in one aspect of the present invention an adhesive composition is provided comprising a blend of a hydrophilic pressure sensitive adhesive (PSA) (Component I) and a hydrophobic PSA (Component II). Suitable adhesive blend compositions of the present invention comprise a Component I to Component II weight ratio of from about 1:19 to about 19:1 (approximately 5/95 and 95/5 weight percent); preferable adhesive compositions comprise a Component I to Component II weight ratio of from about 1:9 to about 9:1 (approximately 10/90 and 90/10 weight percent); more preferable adhesive compositions comprise a Component I to Component II weight ratio of from about 1:4 to about 4:1 (approximately 20/80 and 80/20 weight percent); and most preferable adhesive compositions comprise a Component I to Component II weight ratio of from about 1:3 to about 3:1 (approximately 25/75 and 75/25 weight percent).
The present invention provides an adhesive composition comprising a blend of a hydrophilic PSA and a hydrophobic PSA, wherein the hydrophilic component comprises the polymerization product of (a) about 15 to about 85 parts by weight of an (meth)acrylate ester monomer wherein the (meth)acrylate ester monomer, when polymerized, has a glass transition temperature (Tg) of less than about 10xc2x0 C.; (b) about 85 to about 15 parts by weight of a hydrophilic acidic comonomer; and (c) at least about 10 parts based on 100 parts of the sum of components (a)+(b) of a non-reactive plasticizing agent and wherein the hydrophobic component is an elastomer or thermoplastic elastomer including but not limited to styrene block copolymers (e.g., linear, radial, tapered, star) consisting of copolymerized styrene and isoprene, butadiene or ethylene-butylene; polyisoprene; polybutadiene; polyisobutylene; butyl rubber; styrene-butadiene rubber; natural rubber; and poly-xcex1-olefins (e.g., polyhexene, polyoctene and propylene-hexene).
Inherently tacky elastomers and thermoplastic elastomers do not require the addition of a tackifying resin or plasticizer, although tackifying resins and plasticizers could be added to the elastomers or thermoplastic elastomer. On the other hand, tackifying resins and/or plasticizers are added to non-tacky elastomers and thermoplastic elastomers to provide the hydrophobic adhesive (Component II). Preferably, when used, tackifying resins and plasticizers are soluble in the elastomers or thermoplastic elastomers of Component II.
Potential additives that may be added to Component I, Component II, or to the blend of components I and II include initiators, chain transfer agents, pigments, fillers, medicinal additives, hollow or solid microspheres (expandable and non-expandable), as well as compatibilizing agents including block copolymers and homopolymers.
In another aspect, adhesive coated articles are provided, such as medical tapes, pavement marking tapes, labels, duct tapes, masking tapes, and other articles useful for dry- and wet-surfaces, such as wound dressings, and surgical drapes.
Advantageously, the blend of hydrophilic PSAs with hydrophobic PSAs provides for an improved balance of adhesion performance to both dry and wet surfaces, particularly for skin surfaces. Preferably, as measured by the Test Protocols described herein, the adhesive articles of the present invention have an initial (T0) adhesion to wet skin and to dry skin of at least about 0.8 N/dm and no greater than about 8.0 N/dm; and have an extended (24 to 48 hours, T24-48) of no greater than about 15 N/dm. Further, the adhesive compositions of the present invention may also have an initial peel adhesive (bond between the adhesive layer and the testing surface) to stainless steel underwater that is at least 16 N/dm, while the two-bond (bond between the adhesive layer and the substrate) is at least 25 N/dm.
In another aspect of the present invention, a method of using the adhesive blends of the present invention is provided comprising the steps of: (a) applying a layer of the adhesive blend to a predetermined thickness onto a substrate, and (b) applying. the layered substrate onto a wet or dry surface. Further, the wet or dry surface is wet or dry skin.
In yet another aspect of the present invention, a pressure sensitive adhesive article is provided comprising a substrate and a pressure sensitive adhesive composition disposed thereon, wherein the pressure sensitive adhesive composition comprises a blend of (I) a hydrophilic pressure sensitive adhesive and (II) a hydrophobic pressure sensitive adhesive, wherein the substrate is selected from the group of cloth, metallized foil, metallized film, polymeric film, nonwoven polymeric material, paper, foam, and combinations thereof
As used herein in this application:
xe2x80x9cpressure-sensitive adhesivexe2x80x9d or xe2x80x9cPSAxe2x80x9d refers to a viscoelastic material that possesses the following properties: (1) aggressive and permanent tack, (2) adherence with no more than finger pressure, (3) sufficient ability to hold onto a substrate, and (4) sufficient cohesive strength to be removed cleanly from the substrate;
xe2x80x9chydrophilic adhesivexe2x80x9d refers to a material that exhibits pressure-sensitive adhesive properties when adhered to a wet substrate. Hydrophilic adhesives may or may not demonstrate pressure-sensitive adhesive properties under dry conditions;
xe2x80x9c(meth)acrylate monomersxe2x80x9d are acrylic acid esters or methacrylic acid esters of non-tertiary alcohols, the alcohols preferably having about 4 to 12 carbon atoms;
xe2x80x9chydrophilic acidic comonomersxe2x80x9d are water soluble ethylenically unsaturated, free radically reactive monomers having carboxylic, sulfonic or phosphonic acid functionality and are copolymerizable with the (meth)acrylate monomers;
xe2x80x9ccompatiblexe2x80x9d when referring to plasticizing agents (as used in Component I) means plasticizing agents that:
1) exhibit no gross phase separation from the hydrophilic adhesive when present in the prescribed amounts,
2) once mixed with the hydrophilic adhesive, do not significantly phase separate from the hydrophilic adhesive upon aging,
3) function as a rheological modification agent for the hydrophilic adhesive, such that this plasticized adhesive exhibits pressure-sensitive properties as defined above, and
4) promote high conversion polymerization, that is greater than 98% polymerization of the comonomers;
xe2x80x9cnon-reactivexe2x80x9d refers to plasticizing agents that do not contain free radically reactive ethylenically unsaturated groups that could co-react with the comonomers or functionalities that significantly inhibit the polymerization of these monomers;
xe2x80x9cnon-volatilexe2x80x9d refers to plasticizing agents that, when present in the hydrophilic adhesive, generate less than 3% VOC (volatile organic content). The VOC content can be determined analogously to ASTM D 5403-93 by exposing the coated hydrophilic adhesive to 100xc2x0xc2x15xc2x0 C. in a forced draft oven for 1 hour. If less than 3% plasticizing agent is lost from the plasticized pressure-sensitive adhesive, then the plasticizing agent is considered xe2x80x9cnon-volatilexe2x80x9d;
xe2x80x9csolventlessxe2x80x9d refers to hydrophilic adhesive polymerizable mixtures that are essentially 100% solid systems. Usually, such polymerizable mixtures have no more than about 5% organic solvents or water, more typically no more than about 3% organic solvents or water. Most typically, such polymerizable mixtures are free of organic solvents and water.
Adhesives blends of the present invention uniquely balance dry- and wet-surface adhesion characteristics and comprise a hydrophilic PSA (Component I) and a hydrophobic PSA (Component II). The adhesive blends can optionally include additives.
Component I comprises a hydrophilic wet-stick polyacrylate PSA comprising the polymerization product of: at least one (meth)acrylate monomer, at least one hydrophilic acidic comonomer, and at least one plasticizing agent. Furthermore, the polymerizable mixture typically contains additional additives, including initiators, chain transfer agents, and/or other additives, such as pigments, glass or polymeric bubbles or beads (which may be expanded or unexpanded), fibers, reinforcing agents, hydrophobic or hydrophilic silica, toughening agents, fire retardants, antioxidants, finely ground polymeric particles such as polyester, nylon, and polypropylene, and stabilizers.
(Meth)acrylate Monomer
The hydrophilic PSAs used as a component of the adhesive blends of the present invention contain at least one monofunctional unsaturated monomer selected from the group consisting of (meth)acrylate esters of non-tertiary alkyl alcohols, the alkyl groups of which preferably comprise from about 4 to about 12 carbon atoms, more preferably about 4 to about 8 carbon atoms; and mixtures thereof. Preferred (meth)acrylate monomers have the following general Formula (I): 
wherein R1 is H or CH3. R2 is selected from linear or branched hydrocarbon groups and may contain one or more heteroatoms. The number of carbon atoms in the hydrocarbon group is preferably about 4 to about 12, and more preferably about 4 to about 8.
Examples of suitable (meth)acrylate monomers useful in the present invention include, but are not limited to, n-butyl acrylate, decyl acrylate, 2-ethylhexyl acrylate, hexyl acrylate, isoamyl acrylate, isodecyl acrylate, isononyl acrylate, isooctyl acrylate, lauryl acrylate, 2-methyl butyl acrylate, 4-methyl-2-pentyl acrylate, ethoxy ethoxyethyl acrylate and mixtures thereof. Particularly preferred are n-butyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, lauryl acrylate, and mixtures thereof
Hydrophilic Acidic Comonomer
Useful hydrophilic acidic comonomers include, but are not limited to, those selected from ethylenically unsaturated carboxylic acids, ethylenically unsaturated sulfonic acids, ethylenically unsaturated phosphonic acids, and mixtures thereof. Examples of such comonomers include those selected from acrylic acid, methacrylic acid, itaconic acid, fumaric acid, crotonic acid, citraconic acid, maleic acid, xcex2-carboxyethyl acrylate, 2-sulfoethyl methacrylate, styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, vinyl phosphonic acid, and the like, and mixtures thereof. Particularly preferred hydrophilic acidic monomers are ethylenically unsaturated carboxylic acids, most preferably, acrylic acid.
Minor amounts (e.g., not greater than about 10% by weight) of monomers copolymerizable with both the (meth)acrylate monomers and hydrophilic acidic monomers can be used. Examples of such monomers include (meth)acrylamides, vinyl esters and N-vinyl lactams.
The copolymerizable mixture used to make the hydrophilic adhesive comprises, based upon 100 parts by weight total, about 15 to about 85 parts by weight of at least one (meth)acrylate monomer and about 85 to about 15 parts by weight of a hydrophilic acidic comonomer. Preferably, the copolymerizable mixture comprises about 20 to about 80 parts by weight of at least one (meth)acrylate monomer and about 80 to about 20 parts by weight of a hydrophilic acidic comonomer. More preferably, the copolymerizable mixture comprises about 40 to about 60 parts by weight of at least one (meth)acrylate monomer and about 60 to about 40 parts by weight of a hydrophilic acidic comonomer. The ratio of each comonomer in the hydrophilic adhesive can be chosen to optimize the performance.
Plasticizing Agent
Useful plasticizing agents are compatible with the starting monomers and the resultant polymers of the hydrophilic pressure sensitive adhesive, such that once the plasticizing agent is mixed with the monomers or the resulting polymers, the plasticizing agent does not phase separate. By xe2x80x9cphase separationxe2x80x9d or xe2x80x9cphase separatexe2x80x9d, it is meant that by differential scanning calorimetry (DSC) no detectable thermal transition, such as a melting or glass transition temperature, can be found for the pure plasticizing agent in the wet stick adhesive composition.
Preferably, the plasticizing agent is non-volatile and non-reactive. Particularly useful plasticizing agents include polyalkylene oxides having weight average molecular weights of about 150 to about 5,000, preferably of about 150 to about 1,500, such as polyethylene oxides, polypropylene oxides, polyethylene glycols, and copolymers thereof; alkyl or aryl functionalized polyalkylene oxides, such as PYCAL 94 (a phenyl ether of polyethylene oxide, commercially available from ICI Chemicals); benzoyl functionalized polyethers, such as Benzoflex 400 (polypropylene glycol dibenzoate, commercially available from Velsicol Chemicals) and monomethyl ethers of polyethylene oxides, and mixtures thereof. Examples of other useful plasticizing agents include CARBOWAX(trademark) MPEG 550, a methoxypolyethylene glycol plasticizer having a molecular weight of approximately 550 and available from Union Carbide Corp.; Polyol PPG 1025, a polypropylene glycol plasticizer having a molecular weight of approximately 1025 and available from Lyondell Chemical Worldwide, Inc.; Polyol PPG 425, a polypropylene glycol plasticizer having a molecular weight of approximately 425 and available from Lyondell Chemical Worldwide, Inc.; and PLURONIC(trademark) 25R4, an ethylene oxide/propylene oxide block copolymer plasticizer available from BASF Company.
The plasticizing agent can be used in amounts of at least about 10 pph (parts by weight per 100 parts of the (meth)acrylate monomers and hydrophilic acidic comonomers). Typically, the plasticizing agent is present in the adhesive in amounts from about 15 to 100 pph. Preferably, the plasticizing agent is present in amounts from about 20 to 80 pph. The amount of plasticizer required depends upon the type and ratios of the (meth)acrylate monomers and hydrophilic acidic comonomers employed in the polymerizable mixture and the chemical class and molecular weight of the plasticizing agent.
Additives
A. Initiators
A free radical initiator is preferably added to aid in the copolymerization (meth)acrylate comonomers and acidic comonomers. The type of initiator used depends on the polymerization process. Photoinitiators which are useful for polymerizing the polymerizable mixture monomers include benzoin ethers such as benzoin methyl ether or benzoin isopropyl ether, substituted benzoin ethers such as 2-methyl-2-hydroxypropiophenone, aromatic sulfonyl chlorides such as 2-naphthalenesulfonyl chloride, and photoactive oxides such as 1-phenyl-1,1-propanedione-2-(o-ethoxycarbonyl)oxime. Examples of commercially available photoinitiators are IRGACURE(trademark) 651 (2,2-dimethoxy -1,2-diphenylethane-1-one) and IRGACURE(trademark) 184 (a hydroxycyclohexyl phenyl ketone), both commercially available from Ciba-Geigy Corporation. Generally, the photoinitiator is present in an amount of about 0.005 to 1 weight percent based on the weight of the copolymerizable monomers. Examples of suitable thermal initiators include AIBN (2,2xe2x80x2-azobis(isobutyronitrile), hydroperoxides, such as tert-butyl hydroperoxide, and peroxides, such as benzoyl peroxide and cyclohexane peroxide. Depending on the particular initiator used, the product resulting from the copolymerization reaction may further comprise a residue of the polymerization initiator.
B. Chain Transfer Agents
Preferably, the polymerizable mixture also includes a chain transfer agent to control the molecular weight of the polymerized compositions. Chain transfer agents are materials that regulate free radical polymerization and are generally known in the art. Suitable chain transfer agents include halogenated hydrocarbons such as carbon tetrabromide; sulfur compounds such as lauryl mercaptan, butyl mercaptan, ethanethiol, isooctylthioglycolate (IOTG), 2-ethylhexyl thioglycolate, 2-ethylhexyl mercaptopropionate, 2-mercaptoimidazole, and 2-mercaptoethyl ether and mixtures thereof
The amount of chain transfer agent that is useful depends upon the desired molecular weight and the type of chain transfer agent. The chain transfer agent is typically used in amounts from about 0.001 part to about 10 parts by weight per 100 parts of total monomer, and preferably from about 0.01 part to about 0.5 part, and most preferably from about 0.02 part to about 0.20 part.
C. Other Additives
Other additives can be included in the polymerizable mixture to change the properties of the adhesive. Such additives include fillers, pigments, chemical or physical blowing agents, anti-microbials, antibiotics, medicinal additives, glass or polymeric bubbles or beads (which may be expanded or unexpanded), fibers, reinforcing agents, hydrophobic or hydrophilic silica, toughening agents, fire retardants, antioxidants, finely ground polymeric particles such as polyester, nylon, and polypropylene, and stabilizers. Crosslinking agents could also be added, such as copolymerizable mono-ethylenically unsaturated aromatic ketone comonomers free of ortho-aromatic hydroxyl groups such as those disclosed in U.S. Pat. No. 4,737,559. Specific examples of useful crosslinking agents include para-acryloxybenzophenone, para-acryloxyethoxybenzophenone, para-N-(methylacryloxyethyl)-carbamoylethoxybenzophenone, para-acryloxyacetophenone, ortho-acrylamidoacetophenone, acrylated anthraquinones, and the like. A preferred crosslinking agent is acryloyloxybenzophenone. When used, additives are added in amounts sufficient to affect the desired end properties, as known to those skilled in the art.
Methods
A method for preparing a hydrophilic pressure sensitive adhesive comprises the steps of:
(a) combining a polymerizable mixture comprising:
(i) about 15 to about 85 parts by weight of an (meth)acrylate ester monomer wherein the (meth)acrylate ester monomer, when homopolymerized, has a Tg of less than about 10xc2x0 C.;
(ii) about 85 to about 15 parts by weight of a hydrophilic acidic comonomer; and
(iii) at least about 10 parts based on 100 parts of the sum of components (a)+(b) of a non-reactive plasticizing agent; and
(b) polymerizing the polymerizable mixture to form a pressure sensitive adhesive that adheres to wet substrate surfaces.
An alternative method for preparing a hydrophilic pressure sensitive adhesive comprises the steps of:
(a) combining a polymerizable mixture comprising:
(i) about 15 to about 85 parts by weight of an (meth)acrylate ester monomer wherein the (meth)acrylate ester monomer, when homopolymerized, has a Tg of less than about 10xc2x0 C.;
(ii) about 85 to about 15 parts by weight of a hydrophilic acidic comonomer; and
(iii) at least about 10 parts based on 100 parts (a)+(b) of a non-reactive plasticizing agent;
(b) enveloping the polymerizable mixture in a packaging material; and
(c) exposing the enveloped polymerizable mixture to radiation sufficient to polymerize the polymerizable mixture and to form a pressure sensitive adhesive that adheres to wet substrate surfaces.
Yet another method for preparing a hydrophilic pressure sensitive adhesive comprises the steps of:
(a) preparing a prepolymeric syrup comprising:
(i) about 15 to about 85 parts by weight of an (meth)acrylate ester monomer wherein the (meth)acrylate ester monomer, when homopolymerized, has a Tg of less than about 10xc2x0 C.; and
(ii) about 85 to about 15 parts by weight of a hydrophilic acidic comonomer;
(b) combining the prepolymeric syrup with at least about 10 parts based on 100 parts of the sum of components (i)+(ii) of a non-reactive plasticizing agent to form a polymerizable mixture; and
(c) exposing the polymerizable mixture to radiation sufficient to polymerize the polymerizable mixture and to form a pressure sensitive adhesive that adheres to wet substrate surfaces.
Polymerization Processes
Polymerization methods, such as the continuous free radical polymerization method described in U.S. Pat. Nos. 4,619,979 and 4,843,134; the essentially adiabatic polymerization methods using a batch reactor described in U.S. Pat. No. 5,637,646; and, the methods described for polymerizing packaged polymerizable mixtures described in U.S. Pat. No. 5,804,610 may be utilized to prepare the polymers.
Polymerization can also be effected by exposure to ultraviolet (UV) radiation as described in U.S. Pat. No. 4,181,752.
Component II comprises a hydrophobic PSA that includes an elastomer or thermoplastic elastomer and, optionally, a tackifying resin and/or plasticizer.
Thermoplastic Elastomer
Thermoplastic elastomeric materials are generally defined as materials that behave as elastomers at ambient temperatures, but are thermoplastic at elevated temperatures where they can be molded and remolded. Thermoplastic elastomeric materials useful in the present invention include, for example, linear, radial, star and tapered styrene-isoprene block copolymers such as Kraton(trademark) D 1107 and Kraton(trademark) D1113, both available from Shell Chemical Co., Houston, Tex.; EUROPRENE(trademark) SOL TE 9110, available from EniChem Elastomers Americas, Inc., Houston, Tex.; linear styrene-(ethylene-butylene) block copolymers such as Kraton(trademark) G1657, available from Shell Chemical Co.; linear styrene-(ethylene-propylene) block copolymers such as Kraton(trademark) G1701, available from Shell Chemical Co.; linear, radial, and star styrene-butadiene block copolymers such as Kraton(trademark) D 1118X, available from Shell Chemical Co.; EUROPRENE(trademark) SOL TE 6205, available from EniChem Elastomers Americas, Inc.; polyetheresters, such as HYTREL(trademark) G3548, available from DuPont; poly-alpha-olefin-based thermoplastic elastomeric materials such as those represented by the formula xe2x80x94(CH2xe2x80x94CHR)xe2x80x94, where R is an alkyl group containing 2 to 10 carbon atoms; and poly-alpha-olefins based on metallocene catalysis, such as ENGAGE(trademark) EG8200, an ethylene/poly-alpha-olefin copolymer available from Dow Plastics Co., Midland, Mich.
B. Elastomer
Elastomeric materials are materials that generally form one phase at 21xc2x0 C., have a glass transition temperature less than about 0xc2x0 C., and exhibit elastic properties. Elastomers are among the group of polymers that can easily undergo very large, reversible elongations (up to 500 to 1000%) at relatively low stresses. Elastomeric materials useful in the present invention include, for example, natural rubbers such as CV-60, a controlled viscosity grade, and SMR-5, a ribbed smoked sheet rubber; butyl rubbers, such as Exxon Butyl 268 available from Exxon Chemical Co.; synthetic polyisoprenes such as Kraton(trademark) IR305, available from Shell Chemical Co.; NATSYN(trademark) 2210, available from Goodyear Tire and Rubber Co.; ethylene-propylenes; polybutadienes; polyisobutylenes, such as VISTANEX(trademark) MM L-80, available from Exxon Chemical Co.; and styrene-butadiene random copolymer rubbers such as AMERIPOL(trademark) 1011A, available from B F Goodrich, Akron, Ohio.
C. Tackifying Resin or Plasticizer
Optionally, these thermoplastic elastomeric or elastomeric materials can be modified with tackifying resins or plasticizers.
The tackifying resins or plasticizers may or may not be miscible with Component I. A tackifying resin or plasticizer, when present generally comprises about 5 to 300 parts by weight, more typically up to about 200 parts by weight, based on 100 parts by weight of the elastomer or the thermoplastic elastomer. Useful examples of tackifying resins suitable for the invention include but are not limited to liquid rubbers, aliphatic and aromatic hydrocarbon resins, rosin, natural resins such as dimerized or hydrogenated balsams and esterified abietic acids, polyterpenes, terpene phenolics, phenol-formaldehyde resins, and rosin esters. Preferred tackifying resins include Escorez(trademark) 1310LC available from Exxon Chemical Co. and Wingtack(trademark) 95 available from Goodyear Tire and Rubber Co. Useful examples of plasticizers include but are not limited to polybutene, paraffinic oils, naphthenic oils, petrolatum, and certain phthalates with long aliphatic side chains such as ditridecyl phthalate.
Additives such as pigments, fillers, medicinals (e.g., antimicrobials and other biologically active agents), crosslinkers, and antioxidants may be used in the adhesive blends of the present invention. Examples of fillers include but are not limited to inorganic fillers such as zinc oxide, alumina trihydrate, talc, titanium dioxide, aluminum oxide and silica. Other additives such as amorphous polypropylene or various waxes may also be used. Pigments and fillers may be incorporated into the adhesive blend in order to manipulate the properties of the adhesive according to its intended use. Radiation crosslinkers such as benzophenone, derivatives of benzophenone, and substituted benzophenones may be added to the adhesive blends of the invention. Finally, antioxidants may be used to protect against severe environmental aging caused by ultraviolet light or heat. Antioxidants include, for example, hindered phenols, amines, and sulfur and phosphorous hydroxide decomposers. A preferred antioxidant is IRGANOX(trademark) 1010 available from Ciba-Geigy Corp.
Although Components I and II are preferably blended and coated using melt extrusion techniques or by solvent coating, blending can be done by any method that results in a substantially homogeneous distribution of Components I and II.
If a hot melt coating is desired, a blend is prepared by melt mixing the components in the molten or softened state using devices that provide dispersive mixing, distributive mixing, or a combination of dispersive and distributive mixing. Both batch and continuous methods of blending may be used. Examples of batch methods include Brabender(trademark) or Banbury(trademark) internal mixing, and roll milling. Examples of continuous methods include single screw extruding, twin screw extruding, disk extruding, reciprocating single screw extruding, and pin barrel single screw extruding. The continuous methods can include both distributive elements such as cavity transfer elements such as CTM(trademark), available from RAPRA Technology, Ltd., Shrewsbury, England, pin mixing elements, and static mixing elements and dispersive elements such as Maddock mixing elements or Saxton mixing elements.
An example of a batch process is the placement of a portion of the blend between the desired substrate to be coated and a release liner, pressing this composite structure in a heated platen press with sufficient temperature and pressure to form a pressure-sensitive coating of the desired thickness and cooling the resulting coating.
Continuous forming methods include drawing the pressure-sensitive adhesive composition out of a film die and subsequently contacting a moving plastic web or other suitable substrate. A related continuous method involves extruding the pressure-sensitive adhesive composition and a coextruded backing material from a film die and subsequently cooling to form a pressure-sensitive adhesive tape.
Other continuous forming methods involve directly contacting the pressure-sensitive adhesive blend to a rapidly moving plastic web or other suitable substrate. In this method, the pressure-sensitive adhesive blend can be applied to the moving web using a die having flexible die lips such as a reverse orifice-coating die. After forming, the pressure-sensitive adhesive coatings are solidified by quenching using both direct methods, such as chill rolls or water baths, and indirect methods, such as air or gas impingement.
Optionally, Components I and II are blended and coated using solvent blending and solvent coating techniques. However, it is preferable that Components I and II be substantially soluble in the solvents used. Mixing can be done by any method that results in a substantially homogeneous distribution of Component I and Component II.
The adhesive blends of the present invention are useful to prepare adhesive coated articles. The present invention provides adhesives that are skin-compatible and thus are particularly suitable for medical applications, such as surgical tapes and drapes, bandages, athletic tapes, wound dressings and the like. The adhesive blends may be coated onto any backing suitable for medical applications including occlusive (substantially non-breathable) and non-occlusive backings (breathable). Occlusive backings are also known as low porosity backings. Nonlimiting examples of occlusive backings include films, foams and laminates thereof Nonlimiting examples of non-occlusive backings include woven substrates, knit substrates, nonwoven substrates such as hydroentangled materials or melt blown webs, foams and thermally embossed nonwoven substrates.
The coated adhesive blends of the present invention can be crosslinked by exposure to ultraviolet radiation from, for example, medium pressure mercury arc lamps, or by exposure to an electron beam (e-beam). For example, coated adhesive blends can be irradiated with E-beam radiation at a level of 2 Mrad dosage at 175 kV directly after and in-line with the coating process using an ELECTOCURTAIN(trademark) CB-175 electron beam system available from Energy Sciences, Inc., Wilmington, Mass..